The use of miniaturized electrical systems (microsystems) on the order of 1 cm2 has been proposed to provide distributed sensing capability. Microsystem sensors can be used to monitor various environmental and operational conditions and transmit signals back to a host receiver for many different applications, such as industrial monitoring, security applications, weather prediction, and so on. The design and implementation of such devices and systems requires overcoming several challenges, such as designing small and robust packaging and providing adequate transmitter power. A major consideration in designing such systems remains providing adequate electrical power, and for many microsystems, this challenge remains a significant obstacle. In general, current miniature battery technologies cannot store enough energy to power these systems for long periods of time, such as on the order of months. Another disadvantage of battery use is that many sensor applications involve harsh or limited access environments that can limit or disable battery performance and/or render battery maintenance virtually impossible.
One approach to overcome the problem of providing enough battery power for Microsystems is to extract energy from the surrounding environment. This approach, which is called energy harvesting (or scavenging) eliminates the need for an external or stored power supply, thus allowing a system to be made fully autonomous, that is, one that requires no external power connections or maintenance. As long as the source of environmental energy is available, an energy harvesting microsystem can remained fully powered, virtually non-stop, while providing information to the user.
Several techniques have been proposed and developed to extract energy from the environment. The most common available sources of energy are vibration, temperature, and stress (pressure). In many environmental applications, vibration energy may be the most readily available and easiest to convert into electricity. In general, vibration energy can be converted into electrical energy using one of three techniques: electrostatic charge, magnetic fields, and piezoelectric materials. Piezoelectric generation of electricity from vibration energy typically represents the most cost-effective approach, as the electrostatic and magnetic techniques usually require more extensive design, packaging, and integration work to adapt to particular applications.
Current methods of manufacturing small piezoelectric energy harvesting devices typically involve traditional PC (printed circuit) board techniques in which components are mounted on a PC and then integrated into a separate housing or other structure. Such methods are typically expensive and inefficient when small-scale devices are produced. Moreover, for applications in which vibration energy is converted to electrical energy, a rigid platform for the piezoelectric elements must be provided to maximize energy generation. Present methods of piezoelectric device manufacture typically involve mounting or attaching a piezoelectric beam to a separate case. Even if the bond between the case and beam is strong, the attachment point often represents a source of energy loss due to vibrational transmission and/or losses in the interface region.